Water from outside showers are a gray area.

We have one of those teepee shower tents that we used for the honey bucket before we had a cassette toilet.  The bottom will hold the water, so it shouldn't take much to rig up some type of collection system to drain it into a bucket.  Put the teepee on higher ground, cut a corner off, a little duct tape on a hose connector and drain to a bucket at a lower point.  Or, you can use Jim's idea, and add a little deodorant.  ;D